1. Field of the Invention
This invention relates to actuation mechanisms used in or with apparatuses, machines, appliances and like devices which when activated result in engagement of a component of the device with another component thereof or of another apparatus, machine or appliance. More particularly, this invention relates to actuator mechanisms used in or with the aforesaid devices as components thereof which possess elastic properties and are so formed that when subjected to axial stress undergo an elastic deformation causing an axial deplacement of a movable body component operatively connected to the mechanism thereby effectuating an engagement of the body component with another component of the apparatus, machine or appliance. The actuator, when the stress is removed automatically regains its unstressed form and the displaced body returns to its former position, simultaneously disengaging from the other component.
In a preferred use in a brake assembly of a vehicle, the movable body is the brake pad or shoe of a disc brake which, when displaced by the stressed actuator, frictionally engages the rotating disc of the brake assembly whose rotational motion is to be restrained and applies a braking force thereagainst.
Briefly, this invention utilizes a plurality of rigid and resilient members which are bonded together and formed into an integral unit capable of being retained in a housing of the assembly in sealing relation therein so that when a pressurizing fluid is admitted, the unit undergoes an axial deformation in which the inner members shift axially relative to the outer members of the plurality of members and a displacement of the movable brake pad or shoe connected thereto results.
2. Description of the Prior Art
Actuators and actuation devices in general for creating movements in apparatuses, machines and appliances and their component parts are well known. For example, in a disc brake assembly as mentioned previously, and for which the present invention has especial utility and suitability, hydraulic fluid pressure is used to drive a piston in a cylinder in the brake caliper thereof to urge a friction pad against a brake disc or rotor fixed to the wheels of a vehicle, thereby braking the vehicle. Exemplary patents disclosing this type of actuation device are U.S. Pat. No. 4,274,514 in which a pair of friction pads are forced into engagement with the rotor of a disc brake assembly by hydraulic fluid acting against a piston mounted in the caliper assembly of the brake, and U.S. Pat. No. 4,261,443 also disclosing a hydraulic piston and cylinder actuator for urging a brake pad against a rotor or brake disc.
Other prior art actuation devices exist in which a flexible piston capable of axial expansion and contraction is used to effect engagement and disengagement of a brake pad from a brake disc. For example, U.S. Pat. No. 4,306,639 discloses a disc brake in which a molded, hollow expansible piston is sealingly retained in a caliper of a brake assembly. Hydraulic pressure in the interior of the piston causes axial expansion of the piston and a brake pad attached exteriorly to the piston is urged against the brake disc. A return spring in the piston is required to retract the piston when the pressure is relieved.
In U.S. Pat. No. 4,077,499 a "spring pipe" is employed which carries a brake pad on one end thereof and hydraulic pressure applied to the interior of the spring pipe causes axial expansion thereof and urges the brake pad against a rotor disc adjacent thereto. When the pressure is relieved, the spring pipe contracts and disengages the brake pad from the rotor. U.S. Pat. Nos. 3,675,743 and 3,666,059 on the other hand disclose bellows-type actuation devices having corrugated side walls that are inelastically deformable such that when extended by pressure interiorly applied to the bellows, the inelastic deformations of the walls prevents the actuators from rebounding to their original length when the pressure is relieved. In this way, the brake pad lining wear is automatically compensated for by the progressive increase in relaxed length of the bellows wall of the actuator.
Structures generally corresponding to that contemplated for use in the present invention have been known to some extent for some time for use as load supports and bearings, particularly static load bearings, thrust bearings, and like support means, in shock absorbers and other related applications. Exemplary patents disclosing structure used in devices of this type include U.S. Pat. No. 2,900,182 disclosing static load bearings constructed from layers from elastomeric material interspersed between sheets of metal and bonded together to form a stack of laminations. In this manner, a bearing is formed which has high compressive resistance and low resistance to shear forces. A cannister or retainer is used to encase the stack and prevent extrusion of the elastomeric layers when the device is compressed. Other patents to the same inventor, U.S. Pat. Nos. 3,083,065 and 3,228,673 disclose similiar devices in which laminations of elastomer and metal are used in static load bearings. The first mentioned patent discloses a laminated bearing which overcomes the problems of the earlier device of lateral bulging under compressive stress such as a columnar load, particularly in "tall" stack bearings, by preforming the layers into specific shapes. In this patent the metal layers are "contoured" to oppose uncontrolled lateral shifting. Thus, lateral force components are better contained and bulging is reduced. The latter mentioned patent, the original application of which was filed simultaneously with U.S. Pat. No. 3,083,065, is directed to solving the same problem and utilizes additional peripheral retaining means to improve the bearing resistance to the same uncontrolled lateral shifting under shear stress.
Other prior art patents which disclose similar devices, also directed to the use of the basic structure of a load support bearing of one type or another, are the following: U.S. Pat. No. 2,982,536, disclosing a load bearing in the form of a laminated spring adapted to compress under load and expand laterally; U.S. Pat. No. 3,113,769 disclosing a vehicle load support mounting device including a yieldable body between rigid sleeve members, the yieldable body subjected to torque under empty vehicle conditions and shear, compression and/or tension under loaded vehicle conditions; U.S. Pat. No. 3,377,110 disclosing an elastomer and metal sandwich-like structure for a bushing connecting oscillating elements of a track used on a track laying vehicle; U.S. Pat. No. 3,390,899 disclosing a laminated flexible rocket nozzle and/or pipe joint and bearing therefor utilizing generally the same construction; U.S. Pat. No. 2,995,907 disclosing a universal joint or shaft coupling using internested, spirally wound strips of resilient metal material, the inner and outer ends of which are respectively attached to a hub secured on one shaft and a cup secured to a connected shaft with a continuous mass of solid lubricant or elastomer filling the spaces between the surfaces of the strips; and U.S. Pat. No. 3,787,102 disclosing a load bearing made from alternate layers of elastomer and steel bonded together and contained in an outer bearing support or collar. Other patents disclosing similar devices, to round out the art, are U.S. Pat. No. 3,429,622 illustrating flexible bearings in a rocket nozzle; U.S. Pat. No. 3,690,639, illustrating a helically wound, cylindrial, torsional load bearing; U.S. Pat. No. 3,179,400 illustrating a torsion spring bearing in a wheel suspension system; and, U.S. Pat. No. 3,696,999 illustrating a flexible joint of a rocket motor nozzle.
Notwithstanding the fact that some problems attending the use of actuators of the prior art are not particularly severe, such problems as high costs relating directly to the necessity of using precision manufactured parts, the need for dynamic seals and/or seals of exotic materials in sealing systems to prevent leakage which may yet still wear prematurely and, finally, the difficulties encountered in making repairs and replacements, it has been found that there is a need for a low cost, relatively simple to manufacture device which can be easily installed and which, when used in brake assemblies and other apparatuses, machines and appliances will last throughout the life of the brake pad itself and beyond.
Owing to its novel form when used in actuator devices coupled with its relatively simple construction, the present invention inherently is easy to manufacture and assemble and provides a ready replacement means particularly as a subassembly of a main or larger assembly and requires no dynamic seals, since only a single static "O" ring seal is needed. Additional advantages include fewer parts to wear and/or fail and the elimination of separate return springs and the like.